Copied from upstream:
https://hg.mozilla.org/releases/mozilla-esr38/raw-rev/c1d67bd4c993

# HG changeset patch
# User Timothy Nikkel <tnikkel@gmail.com>
# Date 1454023801 21600
# Node ID c1d67bd4c993b9e344c68954e6f0392c82b81e38
# Parent  530559abe159d3c23f078d673d30ff03d9c244e2
Bug 1224979 - Check if we compute usable filters for the downscaler, and if not put the downscaler in error state so it's not used. r=edwin, a=al

diff --git a/image/Downscaler.cpp b/image/Downscaler.cpp
new file mode 100644
--- /dev/null
+++ b/image/Downscaler.cpp
@@ -0,0 +1,340 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Downscaler.h"
+
+#include <algorithm>
+#include <ctime>
+#include "gfxPrefs.h"
+#include "image_operations.h"
+#include "mozilla/SSE.h"
+#include "convolver.h"
+#include "skia/include/core/SkTypes.h"
+
+using std::max;
+using std::swap;
+
+namespace mozilla {
+namespace image {
+
+Downscaler::Downscaler(const nsIntSize& aTargetSize)
+  : mTargetSize(aTargetSize)
+  , mOutputBuffer(nullptr)
+  , mXFilter(MakeUnique<skia::ConvolutionFilter1D>())
+  , mYFilter(MakeUnique<skia::ConvolutionFilter1D>())
+  , mWindowCapacity(0)
+  , mHasAlpha(true)
+  , mFlipVertically(false)
+{
+  MOZ_ASSERT(gfxPrefs::ImageDownscaleDuringDecodeEnabled(),
+             "Downscaling even though downscale-during-decode is disabled?");
+  MOZ_ASSERT(mTargetSize.width > 0 && mTargetSize.height > 0,
+             "Invalid target size");
+}
+
+Downscaler::~Downscaler()
+{
+  ReleaseWindow();
+}
+
+void
+Downscaler::ReleaseWindow()
+{
+  if (!mWindow) {
+    return;
+  }
+
+  for (int32_t i = 0; i < mWindowCapacity; ++i) {
+    delete[] mWindow[i];
+  }
+
+  mWindow = nullptr;
+  mWindowCapacity = 0;
+}
+
+nsresult
+Downscaler::BeginFrame(const nsIntSize& aOriginalSize,
+                       const Maybe<nsIntRect>& aFrameRect,
+                       uint8_t* aOutputBuffer,
+                       bool aHasAlpha,
+                       bool aFlipVertically /* = false */)
+{
+  MOZ_ASSERT(aOutputBuffer);
+  MOZ_ASSERT(mTargetSize != aOriginalSize,
+             "Created a downscaler, but not downscaling?");
+  MOZ_ASSERT(mTargetSize.width <= aOriginalSize.width,
+             "Created a downscaler, but width is larger");
+  MOZ_ASSERT(mTargetSize.height <= aOriginalSize.height,
+             "Created a downscaler, but height is larger");
+  MOZ_ASSERT(aOriginalSize.width > 0 && aOriginalSize.height > 0,
+             "Invalid original size");
+
+  mFrameRect = aFrameRect.valueOr(nsIntRect(nsIntPoint(), aOriginalSize));
+  MOZ_ASSERT(mFrameRect.x >= 0 && mFrameRect.y >= 0 &&
+             mFrameRect.width >= 0 && mFrameRect.height >= 0,
+             "Frame rect must have non-negative components");
+  MOZ_ASSERT(nsIntRect(0, 0, aOriginalSize.width, aOriginalSize.height)
+               .Contains(mFrameRect),
+             "Frame rect must fit inside image");
+  MOZ_ASSERT_IF(!nsIntRect(0, 0, aOriginalSize.width, aOriginalSize.height)
+                  .IsEqualEdges(mFrameRect),
+                aHasAlpha);
+
+  mOriginalSize = aOriginalSize;
+  mScale = gfxSize(double(mOriginalSize.width) / mTargetSize.width,
+                   double(mOriginalSize.height) / mTargetSize.height);
+  mOutputBuffer = aOutputBuffer;
+  mHasAlpha = aHasAlpha;
+  mFlipVertically = aFlipVertically;
+
+  ReleaseWindow();
+
+  auto resizeMethod = skia::ImageOperations::RESIZE_LANCZOS3;
+
+  skia::resize::ComputeFilters(resizeMethod,
+                               mOriginalSize.width, mTargetSize.width,
+                               0, mTargetSize.width,
+                               mXFilter.get());
+
+  if (mXFilter->max_filter() <= 0 || mXFilter->num_values() != mTargetSize.width) {
+    NS_WARNING("Failed to compute filters for image downscaling");
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  skia::resize::ComputeFilters(resizeMethod,
+                               mOriginalSize.height, mTargetSize.height,
+                               0, mTargetSize.height,
+                               mYFilter.get());
+
+  if (mYFilter->max_filter() <= 0 || mYFilter->num_values() != mTargetSize.height) {
+    NS_WARNING("Failed to compute filters for image downscaling");
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  // Allocate the buffer, which contains scanlines of the original image.
+  // pad by 15 to handle overreads by the simd code
+  size_t bufferLen = mOriginalSize.width * sizeof(uint32_t) + 15;
+  mRowBuffer.reset(new (fallible) uint8_t[bufferLen]);
+  if (MOZ_UNLIKELY(!mRowBuffer)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  // Zero buffer to keep valgrind happy.
+  memset(mRowBuffer.get(), 0, bufferLen);
+
+  // Allocate the window, which contains horizontally downscaled scanlines. (We
+  // can store scanlines which are already downscale because our downscaling
+  // filter is separable.)
+  mWindowCapacity = mYFilter->max_filter();
+  mWindow.reset(new (fallible) uint8_t*[mWindowCapacity]);
+  if (MOZ_UNLIKELY(!mWindow)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  bool anyAllocationFailed = false;
+  // pad by 15 to handle overreads by the simd code
+  const int rowSize = mTargetSize.width * sizeof(uint32_t) + 15;
+  for (int32_t i = 0; i < mWindowCapacity; ++i) {
+    mWindow[i] = new (fallible) uint8_t[rowSize];
+    anyAllocationFailed = anyAllocationFailed || mWindow[i] == nullptr;
+  }
+
+  if (MOZ_UNLIKELY(anyAllocationFailed)) {
+    // We intentionally iterate through the entire array even if an allocation
+    // fails, to ensure that all the pointers in it are either valid or nullptr.
+    // That in turn ensures that ReleaseWindow() can clean up correctly.
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  ResetForNextProgressivePass();
+
+  return NS_OK;
+}
+
+void
+Downscaler::SkipToRow(int32_t aRow)
+{
+  if (mCurrentInLine < aRow) {
+    ClearRow();
+    do {
+      CommitRow();
+    } while (mCurrentInLine < aRow);
+  }
+}
+
+void
+Downscaler::ResetForNextProgressivePass()
+{
+  mPrevInvalidatedLine = 0;
+  mCurrentOutLine = 0;
+  mCurrentInLine = 0;
+  mLinesInBuffer = 0;
+
+  if (mFrameRect.IsEmpty()) {
+    // Our frame rect is zero size; commit rows until the end of the image.
+    SkipToRow(mOriginalSize.height - 1);
+  } else {
+    // If we have a vertical offset, commit rows to shift us past it.
+    SkipToRow(mFrameRect.y);
+  }
+}
+
+static void
+GetFilterOffsetAndLength(UniquePtr<skia::ConvolutionFilter1D>& aFilter,
+                         int32_t aOutputImagePosition,
+                         int32_t* aFilterOffsetOut,
+                         int32_t* aFilterLengthOut)
+{
+  MOZ_ASSERT(aOutputImagePosition < aFilter->num_values());
+  aFilter->FilterForValue(aOutputImagePosition,
+                          aFilterOffsetOut,
+                          aFilterLengthOut);
+}
+
+void
+Downscaler::ClearRow(uint32_t aStartingAtCol)
+{
+  MOZ_ASSERT(int64_t(mOriginalSize.width) > int64_t(aStartingAtCol));
+  uint32_t bytesToClear = (mOriginalSize.width - aStartingAtCol)
+                        * sizeof(uint32_t);
+  memset(mRowBuffer.get() + (aStartingAtCol * sizeof(uint32_t)),
+         0, bytesToClear);
+}
+
+void
+Downscaler::CommitRow()
+{
+  MOZ_ASSERT(mOutputBuffer, "Should have a current frame");
+  MOZ_ASSERT(mCurrentInLine < mOriginalSize.height, "Past end of input");
+
+  if (mCurrentOutLine < mTargetSize.height) {
+    int32_t filterOffset = 0;
+    int32_t filterLength = 0;
+    GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
+                             &filterOffset, &filterLength);
+
+    int32_t inLineToRead = filterOffset + mLinesInBuffer;
+    MOZ_ASSERT(mCurrentInLine <= inLineToRead, "Reading past end of input");
+    if (mCurrentInLine == inLineToRead) {
+      skia::ConvolveHorizontally(mRowBuffer.get(), *mXFilter,
+                                 mWindow[mLinesInBuffer++], mHasAlpha,
+                                 supports_sse2());
+    }
+
+    MOZ_ASSERT(mCurrentOutLine < mTargetSize.height,
+               "Writing past end of output");
+
+    while (mLinesInBuffer == filterLength) {
+      DownscaleInputLine();
+
+      if (mCurrentOutLine == mTargetSize.height) {
+        break;  // We're done.
+      }
+
+      GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
+                               &filterOffset, &filterLength);
+    }
+  }
+
+  mCurrentInLine += 1;
+
+  // If we're at the end of the part of the original image that has data, commit
+  // rows to shift us to the end.
+  if (mCurrentInLine == (mFrameRect.y + mFrameRect.height)) {
+    SkipToRow(mOriginalSize.height - 1);
+  }
+}
+
+bool
+Downscaler::HasInvalidation() const
+{
+  return mCurrentOutLine > mPrevInvalidatedLine;
+}
+
+DownscalerInvalidRect
+Downscaler::TakeInvalidRect()
+{
+  if (MOZ_UNLIKELY(!HasInvalidation())) {
+    return DownscalerInvalidRect();
+  }
+
+  DownscalerInvalidRect invalidRect;
+
+  // Compute the target size invalid rect.
+  if (mFlipVertically) {
+    // We need to flip it. This will implicitly flip the original size invalid
+    // rect, since we compute it by scaling this rect.
+    invalidRect.mTargetSizeRect =
+      IntRect(0, mTargetSize.height - mCurrentOutLine,
+              mTargetSize.width, mCurrentOutLine - mPrevInvalidatedLine);
+  } else {
+    invalidRect.mTargetSizeRect =
+      IntRect(0, mPrevInvalidatedLine,
+              mTargetSize.width, mCurrentOutLine - mPrevInvalidatedLine);
+  }
+
+  mPrevInvalidatedLine = mCurrentOutLine;
+
+  // Compute the original size invalid rect.
+  invalidRect.mOriginalSizeRect = invalidRect.mTargetSizeRect;
+  invalidRect.mOriginalSizeRect.ScaleRoundOut(mScale.width, mScale.height);
+
+  return invalidRect;
+}
+
+void
+Downscaler::DownscaleInputLine()
+{
+  typedef skia::ConvolutionFilter1D::Fixed FilterValue;
+
+  MOZ_ASSERT(mOutputBuffer);
+  MOZ_ASSERT(mCurrentOutLine < mTargetSize.height,
+             "Writing past end of output");
+
+  int32_t filterOffset = 0;
+  int32_t filterLength = 0;
+  MOZ_ASSERT(mCurrentOutLine < mYFilter->num_values());
+  auto filterValues =
+    mYFilter->FilterForValue(mCurrentOutLine, &filterOffset, &filterLength);
+
+  int32_t currentOutLine = mFlipVertically
+                         ? mTargetSize.height - (mCurrentOutLine + 1)
+                         : mCurrentOutLine;
+  MOZ_ASSERT(currentOutLine >= 0);
+
+  uint8_t* outputLine =
+    &mOutputBuffer[currentOutLine * mTargetSize.width * sizeof(uint32_t)];
+  skia::ConvolveVertically(static_cast<const FilterValue*>(filterValues),
+                           filterLength, mWindow.get(), mXFilter->num_values(),
+                           outputLine, mHasAlpha, supports_sse2());
+
+  mCurrentOutLine += 1;
+
+  if (mCurrentOutLine == mTargetSize.height) {
+    // We're done.
+    return;
+  }
+
+  int32_t newFilterOffset = 0;
+  int32_t newFilterLength = 0;
+  GetFilterOffsetAndLength(mYFilter, mCurrentOutLine,
+                           &newFilterOffset, &newFilterLength);
+
+  int diff = newFilterOffset - filterOffset;
+  MOZ_ASSERT(diff >= 0, "Moving backwards in the filter?");
+
+  // Shift the buffer. We're just moving pointers here, so this is cheap.
+  mLinesInBuffer -= diff;
+  mLinesInBuffer = max(mLinesInBuffer, 0);
+  for (int32_t i = 0; i < mLinesInBuffer; ++i) {
+    swap(mWindow[i], mWindow[filterLength - mLinesInBuffer + i]);
+  }
+}
+
+
+
+} // namespace image
+} // namespace mozilla

